X-MINING CWO™ with High Chemical Resistance and Near-Infrared Absorption NIR Absorbing Materials

Sumitomo Metal Mining’s near-infrared absorbing nanoparticles CWO^TM is a characteristic inorganic nanomaterial that has high visible light transmittance and efficiently absorbs near-infrared rays due to the localized surface plasmon resonance absorption and polaron absorption. By using this function, it is widely used as a window for vehicles and buildings, and as a resin additive.

* CWO™ is a registered trademark of Sumitomo Metal Mining. CWO™ is a near-infrared absorbing nanoparticle invented by our company and covered by patents and

trademarks both domestically and internationally. It is a conductive nanoparticle obtained by

adding cesium to tungsten oxide, representing a novel type of thermal absorbing nanoparticle

that we independently developed in 2004. The material technology brand utilizing CWO™ is SOLAMENT™.

In recent years, excellent energy-conversion characteristics (photothermal conversion characteristics) have attracted attention, and it is expected to be adopted in a wide range of fields such as textiles, agriculture, electronics, and optical devices. Therefore, high chemical resistance is also required for use in a wide range of applications.

*1 Plasmon resonance absorption: Absorption of electromagnetic wave energy by the collective resonance of free electrons.

*2 Polaron absorption: Energy absorption caused by the localized electrons when excited to the upper energy levels. The localized electrons are donated from oxygen vacancies and located around W ions.

CWO^TM has high chemical resistance compared to organic materials, so it is applied in many fields. However, there is a problem that the absorption function of near infrared rays is impaired when immersed in a harsh high-temperature alkaline solution.

Therefore, we tried nanoencapsulation of CWO^TM to add the high temperature alkali resistance function. Nanoencapsulation is a method that reduces the surface activity of nanoparticles and suppresses the penetration of water molecules by coating the surface of the nanoparticles with a resin layer. For the encapsulation structure, it is important that the surface of the nanoparticles is densely and uniformly coated with a thick and strong resin layer without gaps. Therefore, we focused on nanoencapsulation by the miniemulsion polymerization method.

By conducting joint research with the Kawaguchi Laboratory of the Graduate School of Organic Materials Science, Yamagata University, we have developed CWO^TM nano capsules that maintain the characteristic functions of CWO^TM and have newly added high chemical resistance. The CWO^TM concentration can be increased up to 40 wt.%.

TEM image of CWO^TM nano capsules

This figure shows the optical profile before and after the chemical resistance (high temperature alkaline solution) test.

Nano-encapsulated CWO^TM that maintains the characteristic functions of CWO^TM and has the function of “withstanding” harsh high-temperature alkaline solutions.

It can be applied to various fields depending on your creations and ideas.